Fix preload ptr field with custom table

[Fs02]

Fix for #215
Related: #198

[codecov]

Codecov Report

Merging #216 (29f1f84) into master (db38ddc) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #216   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           56        56           
  Lines         3940      3928   -12     
=========================================
- Hits          3940      3928   -12     

Impacted Files	Coverage Δ
collection.go	100.00% <100.00%> (ø)
document.go	100.00% <100.00%> (ø)

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